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Hexane solvent extraction without pressing

PostPosted: Thu Feb 05, 2009 6:44 am
by cacofonix
Usually, the algae biomass is first pressed using an oil expeller and a large% of oil is removed.

After that, in order to remove the rest of oil, hexane solvent extraction is used. This process ensures that all the remaining oil are captured by the hexane which can further be distilled and separated from the solvent.

My question is, is it possible to use only the solvent extraction stage alone without the algae pressing stage? Why bother to use hexane solvent extraction only for the last 10%, why not use it for the full 100% of the extraction?

How does this happen in industries such as soybean?

Re: Hexane solvent extraction without pressing

PostPosted: Thu Feb 05, 2009 11:08 am
by phyco
Hai,
To your question there are two reasons 1. Cost 2.Environment protection

Solvent extraction plant is costly compared to expeller press.Energy requirment is also higher for solvent extraction than pressing.

Using solvent extraction will generate waste water which again needs treatment.Using hexane also needs high security.

But in expeller press it is possible to extract only 70 - 80% oil.. the remaining is oil is extracted by hexane solvent keeping the use of hexane as low as possible.

Re: Hexane solvent extraction without pressing

PostPosted: Thu Feb 05, 2009 5:20 pm
by DR Johansen
cacofonix wrote:Usually, the algae biomass is first pressed using an oil expeller and a large% of oil is removed.
After that, in order to remove the rest of oil, hexane solvent extraction is used. ... Why bother to use hexane solvent extraction only for the last 10%, why not use it for the full 100% of the extraction?

Why not just use supercritical CO2 extraction. It is environmentally benign, food safe, and if SC-CO2 can extract oil from half way thru a peanut and the caffiene from a coffee bean, it can surely extract the oil from microalgae without disrupting the wall! And the best part? The seperation method is to drop the pressure on the CO2 to just below the SC point, and the oil just falls right out!

Re: Hexane solvent extraction without pressing

PostPosted: Fri Feb 06, 2009 11:16 am
by phyco
Hai DR.Johansen,
How about the capital cost and operation cost for this method? What about the meal value? i Think Supercritical co2 will extract almost 99.9% of oil out of algae..is possible to use the meal for any other purpose?

Re: Hexane solvent extraction without pressing

PostPosted: Sat Feb 07, 2009 6:52 am
by DR Johansen
There are supercritical CO2 DRY CLEANERS now for heaven sake. It can't be all THAT expensive. Ok, this is not QUITE a true statement. The dry cleaners use liquid CO2 at just shy of SC conditions, but from the relevant web site, I gather the safety factors build into the machines would permit them to run SC.

The point is, while yes it may have a rather steep capital cost, the process is cheap to run and very effective in extracing oils in most cases. I suspect there would be no real need to pre-process the algae, but that is just a guess.

Regarding the remaining "meal" (algae-oils); since SC CO2 processing is "generally regarded as safe", it can be used for food processing for human consumption. I suspect using the meal for animal feed would be just fine.